The image forming systems known in the conventional art include an image forming apparatus such as a printer, photocopier and multi-functional peripheral, and a post-processing apparatus that applies a process of finishing such as punching, folding and binding to the sheets with an image formed thereon by an image forming apparatus.
The post-processing apparatus as an element of the image forming system generally performs on the sheets with an image formed thereon such processes as shifting, punching, binding, folding and bookbinding by gluing. The punching section, the binding section, the folding section and the gluing/bookbinding section are provided with an alignment processing section for aligning the sheets as a pre-processing section for such processing.
This alignment processing section is generally installed inside the post-processing apparatus. This alignment processing section includes an inclined intermediate stacker and a movable regulation member on one side or both sides of the intermediate stacker, and aligns the sheets along the conveyance path for conveying sheets to the binding section or the folding section. To be more specific, sheets are slipped down in the intermediate stacker and are aligned in the sheet conveyance direction. When a preset number of sheets have been stacked on the intermediate stacker, the supply of sheets to the intermediate stacker is suspended, and the movable regulation member then reciprocally moves, so that the sheets are aligned in the width direction with respect to the sheet conveyance direction. This is followed by the finishing step including punching, binding, folding, gluing and bookbinding.
Further, some conventional post-processing apparatuses are provided with a sheet-reversing conveyance section referred to as an intermediate conveyance unit functioning as an intermediate conveyance device and is provided with a sheet width regulation member for aligning the sheet in the width direction (lateral alignment). However, a very small number of sheet-reversing conveyance sections are provided with the device that aligns the sheets in the sheet conveyance direction (longitudinal alignment). In many of the post-processing apparatuses, immediately before finishing steps such as punching, binding and folding, the leading edge or the trailing edge of the sheet is regulated in each of the finishing processes, so that the sheets are longitudinal aligned. Thus, each of the finishing processes needs time to align, and the sheet processing speed is reduced according to the conventional art. Further, in the conventional alignment processing section, conveyance of the succeeding sheet has to be stopped during the finishing operation of the preceding sheet; thus the processing speed of sheet is further reduced, and they are not compatible with the high-speed performance of the main body of the image forming apparatus, with the result that the main body of the image forming apparatus does not take full advantage of its high speed performance. Further, since the conveyance is controlled to be suspended at the time of alignment, the control system is complicated. Thus, stability in the conveyance of sheets is reduced and conveyance failure such as paper jams tends to occur.
In order to solve these problems, disclosed is a technique in which an intermediate conveyance unit is provided as an intermediate conveyance device so as to simultaneously convey a plurality of sheets, whereby the succeeding sheet is aligned even if the preceding sheet is being post-processed (e.g., Unexamined Japanese Patent Application Publication No. 2007-137536).
In the technique disclosed in the Unexamined Japanese Patent Application Publication No. 2007-137536, the intermediate conveyance unit is provided between the image forming apparatus and the post-processing apparatus. A plurality of sheets are reversed and stored there temporarily. These sheets are moved by the sheet push-up member that moves in the vertical direction, whereby a sheet is aligned with the succeeding sheet and their conveyance directions are coordinated.
FIG. 15 is a front cross sectional view of the intermediate conveyance unit B1 equipped with a sheet alignment apparatus disclosed in the Unexamined Japanese Patent Application Publication No. 2007-137536. Referring to FIG. 15, the following describes the structure and the operation of a sheet alignment apparatus as a conventional example, by using the aforementioned intermediate conveyance unit B1.
In FIG. 15, the intermediate conveyance unit B1 as an intermediate conveyance device is provided on the downstream side of the main body of the image forming apparatus in the sheet conveyance direction. A post-processing apparatus FS is installed on the downstream side of the intermediate conveyance unit B1.
The sheet conveyance section of the intermediate conveyance unit B1 includes a sheet carry-in section (the first conveyance section) 11, sheet storage section (the second conveyance section) 12, sheet discharge unit (the third conveyance section) 13, and sheet reversing section (fourth conveyance section) 14.
The sheet carry-in section 11 has a pair of rollers R1 and R2 and a sheet carry-in and conveyance path r11 provided with a guide plate 111. The sheets S ejected from the sheet ejection section 5E of the main body A of the image forming apparatus are sequentially received and conveyed by the sheet carry-in section 11. The sheet storage section 12 is provided with two guide plates 121, a lateral alignment section 122, a sheet push-up member 123 as a sheet push-up section and a sheet storage and conveyance path r12. Two guide plates 121 are arranged parallel to form a sheet storage and conveyance path r12. The sheet storage and conveyance path r12 is a conveyance path for carrying-in and discharging the sheets S to and from the sheet storage section 12. A plurality of sheets S conveyed from the sheet carry-in section 11 are aligned and stored in a state of being stacked in the sheet storage section 12. Sheets are aligned in the sheet conveyance direction between the sheet push-up member 123 and longitudinal alignment member 124, and are then aligned in the width direction by the lateral alignment section 122. After that, the sheets are discharged upward.
The sheet push-up member 123 that stands by staying at the initial stop position P0 and storing the sheets is moved upward along the guide rod 126 and the sheet storage and conveyance path r12 by a motor (not illustrated) as a sheet push-up member moving section. The sheet push-up member 123 thus moves from the initial stop position P0 to the first stop position P1 or the second stop position P2. The leading edge of the first sheet (the preceding sheet) S1 in the sheet carry-in direction is abutted to the sheet abutting plate 123A (to be described later) installed on the sheet push-up member 123. After having been stored, the first sheet S1 is moved to the first stop position P1 by the sheet push-up member 123 that is moving upward. The first stop position P1 refers to the position where the sheet push-up member stops to locate the leading edge of the preceding sheet S1 beyond the tip end of the conveyance path switching section K1 and in the area before the nip portion of the discharge drive roller R5 so as to avoid interruption of the succeeding sheet discharge drive roller R5.
After the sheet push-up member 123 for conveying the preceding sheet S1 has stopped at the first stop position P1, the succeeding sheet S2 is carried in toward the sheet storage section 12 by the rotation of the carry-in drive roller R3. When the sheet push-up member 123 is stopped at the first stop position P1, the leading edge of the preceding sheet does not interfere with the leading edge of the succeeding sheet since the leading edge of the preceding sheet is located above the leading edge of the succeeding sheet S2. After that, the motor-driven sheet push-up member 123 is sent back to the initial stop position P0 when the succeeding sheet is carried into the sheet storage section 12, and the preceding sheet and the succeeding sheet are then stored stacked. When a prescribed number of sheets S have been stored in the sheet storage section 12, the sheet push-up member 123 is again driven, by the sheet push-up member moving section, to the second stop position P2 on the downstream side of the first stop position in the sheet discharge direction and is stopped. The second stop position P2 refers to the position where the sheet push-up member 123 is stopped to cause the sheet S to be aligned in the sheet conveyance direction with the leading edge of the sheet S having reached the position where the leading edge is in contact with the longitudinal alignment member 124. Further, when the sheet push-up member 123 is at this position, the lateral alignment is also performed by the lateral alignment section 122.
A conveyance path switching section K1 is installed at the upper portion of the sheet storage section 12, and serves to switch functions between leading the sheet S into the sheet storage section 12 and discharging the sheet S from the sheet storage section 12. The sheets aligned by the longitudinal alignment member 124 are sandwiched between the discharge drive roller R5 and the driven roller R11 by the switching operation of the conveyance path switching section K1, and are conveyed to the sheet discharge unit 13.
The sheet discharge unit 13 has a sheet conveyance path r13 equipped with a pair of rollers R6 and R7 and a guide plate 131. In the sheet discharge unit 13, a plurality of sheets S stored in the sheet storage section 12 are switched back and conveyed being in the stacked state, and are fed into the succeeding post-processing apparatus FS. This switch-back operation allows the sheets to be discharged with the leading edge and trailing edge of the sheets S reversed, with respect to the direction when the sheets were carried into the sheet storage section 12, in the sheet conveyance direction.
The sheet reversing section 14 has a sheet conveyance path r14 equipped with conveyance rollers R8 and R9 and a guide plate 141. In the sheet reversing section 14, a plurality of sheets S having been stored in the sheet storage section 12 passes through the upper sheet conveyance path r15, and are switched back and reversed again along the sheet conveyance path r14. Passing through the lower sheet conveyance path r16, these sheets are discharged and fed into the succeeding post-processing apparatus FS.
The conveyance path switching section K2 arranged in the sheet discharge unit 13 ensures that the sheets S coming from the sheet storage section 12 are selectively led into the sheet conveyance path r13 for conveying these sheets to the roller pair R6 along the guide plate 13 or into the sheet conveyance path r15 for conveying them to the sheet reversing section 14. The conveyance path switching section K3 arranged on the lower portion of the sheet reversing section 14 switches path between the sheet conveyance path r15 opened by the conveyance path switching section K2 and the sheet conveyance path r16 for ejecting the sheet S from the sheet reversing section 14. The conveyance path switching sections K1, K2 and K3 are connected to solenoids to be driven.
By using the intermediate conveyance unit B1 disclosed in the Unexamined Japanese Patent Application Publication No. 2007-137536, a plurality of sheets placed stacked are longitudinally aligned at a high-speed without interference, without stopping the conveyance of the succeeding sheet even when preceding sheet is being processed.
The sheet push-up member 123 of the sheet storage section 12 for storing the preceding sheet S1 moves to the first stop position P1 before the leading edge of the succeeding sheet S2 enters the sheet storage and conveyance path r12. Accordingly, sheets can be properly placed stacked without interfering with the leading edge the preceding sheet S1.
Regarding the structure disclosed in the Unexamined Japanese Patent Application Publication No. 2007-137536, however, the longitudinal alignment member 124, the solenoid, and the link mechanism for linking the longitudinal alignment member 124 and the solenoid are indispensable in order to align a plurality of sheets stored in the sheet storage section 12 in the sheet conveyance direction. The structure using these components to align the sheets in the sheet conveyance direction increases system production cost.
In order to minimize the system production cost, there is disclosed the technique in which a nip portion is formed between the discharge drive roller R5 and the driven roller (equivalent to the discharge driven roller R11 of FIG. 15). The leading edge of the sheet S is brought into contact with the nip portion to align the sheets in the longitudinal direction (e.g., Unexamined Japanese Patent Application Publication No. 2009-274849). According to the structure of the Unexamined Japanese Patent Application Publication No. 2009-274849, the longitudinal alignment is performed by the nip portion of the discharge drive roller R5 and driven roller. This arrangement eliminates the need of installing a longitudinal alignment member 124, solenoid, and a link mechanism for linking them, with the result that the number of component are reduced, thereby cutting down the production cost.
In the structure of the Unexamined Japanese Patent Application Publication No. 2009-274849, however, the leading edge of the sheets S may be caught in the nip portion between the discharge drive roller R5 and driven roller during longitudinal alignment. Longitudinal alignment and lateral alignment by a lateral alignment section 122 cannot be easily performed simultaneously. If it is impossible to simultaneously perform the longitudinal alignment and the lateral alignment, these alignment processes must be performed separately, with the result that the sheet conveying efficiency will be reduced. Further, if the longitudinal alignment and the lateral alignment are performed at one and the same position using the time lag alone, the pressed contact between the discharge drive roller R5 and the driven roller must be released during the lateral alignment; thus this arrangement requires a complicated structure. In another method, the longitudinal alignment position is shifted from the lateral alignment position, and lateral alignment is performed at a position apart from the nip position between the discharge drive roller R5 and driven roller. There still remains the problem that she two alignment processes cannot be performed simultaneously.